The present invention relates to a modified paper product and a method for making the product. More particularly, the present invention relates to a metallized paper product made by coating a thin metal layer onto a resin-coated paper surface.
While it is known to laminate metal onto a paper substrate, considerable difficulties have been encountered by attempts to deposit an extremely thin film of metal on a paper substrate to provide a useful flexible product. For example, one metallizing method capable of efficiently coating a thin layer of metal on a substrate is the vacuum metallizing process wherein aluminum or other metal is evaporated in a vacuum chamber and condensed onto a surface of the substrate material. However, a paper substrate has a relatively rough surface upon which it is difficult to provide a smooth, thin metal coating. Furthermore, the vacuum levels required in vacuum metallizing processes are extremely low, on the order of 0.0001 Torr, and paper has an inherent affinity for moisture which outgasses as water vapor under such low pressure conditions thereby raising the pressure inside the vacuum chamber. This outgassed water vapor in the chamber must be substantially removed by either freezing or pumping it out in order to maintain a low vacuum condition. Even if it is so removed outgassing interferes with the condensation of metal onto the paper surface.
Efforts to overcome the problems caused by outgassing have included selecting paper substrates having low water content, pre-outgassing paper in separate chambers prior to metallizing and then later restoring water content to the paper, and coating or impregnating paper with clay, waxes or resins applied with solvents. However, none of these efforts have been entirely satisfactory and commercial processes for metallizing of paper have not developed to the same extent as have processes for metallizing plastic films and laminating metal foil to paper, even though these latter processes involve use of more expensive substrates, use of greater amounts of metal, may provide thicker products and have their own process difficulties.
Wherefore, it is an object of the present invention to provide an improved method for providing a thin metal layer on a paper substrate. It is another object of this invention to provide an improved paper product comprising a paper substrate having a thin metal coating thereon. Yet another object of the invention is to provide a method particularly suited for continuous, high speed operation and which is economical and energy efficient. A still further object of this invention is to provide a paper product having good strength and flexibility and which is useful for packaging, decorative and other applications and which has a metallized surface which can be conventionally printed. These and other objects features and advantages will be apparent from the following description and appended claims, taken in conjunction with the accompanying drawing.